Large Patch Lawn Disease

One of my favorite CDs (I know, so 1980’s) is a compilation of hits by the Temptations. While few singers will ever come close to matching the skill and emotion of David Ruffin, I will have to disagree with him when he painfully intones that “I wish it would rain”. We’re about 4 ½ inches above normal for the year, so let’s leave the gloom behind for a little Katrina and the Waves “Walking on Sunshine” action. How’s that for an obscure 1980’s song reference?

Obscure references aside, the changes in the weather make for interesting things happening in the garden.

Early last week large patch – that irritating fungus disease that causes circular areas of our lawn grasses to die – was still at work. We usually talk about large patch being a problem from late summer to mid-fall and early spring. Once the temperatures really warm up, it goes into hiding hanging out in the crowns of the grass. But, the relatively cool and wet weather this spring has kept it active.

Turfgrass researchers at N.C. State University are working on large patch. But, the recommendations haven’t really changed so far. Traditional fungicides such as Heritage and Banner Maxx should be applied around Labor Day and again four to six weeks later. Applications in the spring will stop the development, but will not cure the problem. If you are using liquid products, you need to apply twice as much solution as you do for weed control products (a minimum of 2 gallons per 1000 square feet). Granular fungicides are available and work well.

A new class of fungicides called the SDHI group is finding its way to the marketplace now. These promise to be less expensive and very effective in managing large patch.

Some problems aren’t nearly so easy to spot. I had the opportunity to do some sampling of two older southern magnolias growing side-by-side in a city landscape recently. One looked robust with lots of new growth. The other had new growth but had dropped many of the older leaves and had what tree people call “terminal dieback”. That’s a fancy way of saying that the limbs die from the growing points back toward the main part of the tree.

The list of problems on southern magnolia is pretty short – scale insects and a canker or two. Their root systems are very aggressive and don’t usually fall victim to things in the soil such as nematodes and phytophthora and pythium root rots. Think about how good the root system must be. Have you ever seen a southern magnolia blown over after a tropical system comes through?

When the answer isn’t obvious we start eliminating possibilities. Soil samples taken separately from each tree’s root area are great. Pulling actual leaves and having them analyzed for nutrient content is another step.

In this particular case we did both. The soil samples came back essentially the same. Not much help there. But, the leaf sample showed deficiencies in calcium, manganese and boron. It will be interesting to see if this southern magnolia responds to the nutrients.

Extension professionals and Master Gardeners spend lots of time trying to figure out what’s wrong with your plants and providing science-based recommendations. Sometimes, like with large patch disease, it’s pretty easy to diagnose. Others, like our southern magnolias, take a little more digging.

Our Plant Clinic is open Monday through Friday between 10 am and 4 pm to help you solve garden problems at the New Hanover County Arboretum – 6206 Oleander Drive in Wilmington. Help us out by bringing representative samples of what’s going on. Photographs are often helpful for context. You can also check out our website http://ces.ncsu.edu, where you can post your questions via the ‘Ask an Expert’ link, or contact your local Cooperative Extension center Pender County 259-1238; New Hanover County 798-7660; Brunswick County 253-2610. You can also find great local information at www.nhcarboretum.com and on Facebook. Just search for “New Hanover County Arboretum.